Implantable stimulation devices are devices that generate and deliver electrical stimuli to nerves and tissues for the therapy of various biological disorders, such as pacemakers to treat cardiac arrhythmia, defibrillators to treat cardiac fibrillation, cochlear stimulators to treat deafness, retinal stimulators to treat blindness, muscle stimulators to produce coordinated limb movement, spinal cord stimulators to treat chronic pain, cortical and deep brain stimulators to treat motor and psychological disorders, and other neural stimulators to treat urinary incontinence, sleep apnea, shoulder subluxation, etc. The description that follows will generally focus on the use of the invention within a Spinal Cord Stimulation (SCS) system to treat lower back pain, such as that disclosed in U.S. Pat. No. 6,516,227. However, the present invention may find applicability in any implantable stimulator device
As shown in FIGS. 1A-1C, a SCS system typically includes an Implantable Pulse Generator (IPG) 10, which includes a biocompatible device case 12 formed of a conductive material such as titanium for example. The case 12 typically holds the circuitry and battery 14 (FIG. 2B) necessary for the IPG to function, although IPGs can also be powered via external RF energy and without a battery. The IPG 10 is coupled to electrodes 16 via one or more electrode leads 18, such that the electrodes 16 form an electrode array. The electrodes 16 are carried on a flexible body 20, which also houses the individual signal wires 22 coupled to each electrode. In the illustrated embodiment, there are eight electrodes on lead 18, labeled E1-E8. However, the number of electrodes on a lead, as well as the number of leads, are application specific and therefore can vary. The lead 18 couples to the IPG 10 using a lead connector 24, which is fixed in a non-conductive header material 26, which can comprise an epoxy for example.
As shown in the cross-section of FIG. 2B, the IPG 10 typically includes an electronic substrate assembly including a printed circuit board (PCB) 30 containing various electronic components 32. Two coils (more generally, antennas) are generally present in the IPG 10: a telemetry coil 34 for transmitting/receiving data to/from an external controller 50; and a charging coil 36 for charging or recharging the IPG's battery 14 using an external charger (not shown). (FIG. 1B shows the IPG 10 with the case 12 removed to ease the viewing of the two coils 34 and 36).
FIG. 2A shows a plan view of the external controller 50, and FIG. 2B shows the external controller 50 in relation to the IPG 100 with which it communicates. The external controller 50 is shown as a traditional hand-held patient controller, although it could also comprise a clinician programmer of the type typically used in a clinician's office. (A clinician external controller would look differently, as one skilled in the art understands, and typically comprises computer). The external controller 50 is used to send data to and receive data from the IPG 10. For example, the external controller 50 can send programming data such as therapy settings to the IPG 10 to dictate the therapy the IPG 10 will provide to the patient. Also, the external controller 50 can act as a receiver of data from the IPG 10, such as various data reporting on the IPG's status.
As shown in FIG. 2B, the external controller 50, like the IPG 100, also contains a PCB 52 on which electronic components 54 are placed to control operation of the external controller 50. The external controller 50 is powered by a battery 56, but could also be powered by plugging it into a wall outlet for example.
The external controller 50 typically comprises a user interface 60 similar to that used for a portable computer, cell phone, or other hand held electronic device. The user interface 60 typically comprises touchable buttons 62 and a display 64, which allows the patient or clinician to send therapy programs to the IPG 10, and to review any relevant status information reported from the IPG 10.
Wireless data transfer between the IPG 10 and the external controller 50 preferably takes place via inductive coupling. This typically occurs using a well-known Frequency Shift Keying (FSK) protocol, in which logic ‘0’ bits are modulated at a first frequency (e.g., 121 kHz), and logic ‘1’ bits are modulated at a second frequency (e.g., 129 kHz). To implement such communications, both the IPG 10 and the external controller 50 have communication coils 34 and 58 respectively. Either coil can act as the transmitter or the receiver, thus allowing for two-way communication between the two devices. This means of communicating by inductive coupling is transcutaneous, meaning it can occur through the patient's tissue 70.
The lead 18 in an SCS application is typically inserted into the epidural space 80 proximate to the dura 82 within the patient's spinal cord, as illustrated in cross section in FIG. 3. The proximate portion of the lead 18 is tunneled through the patient where it is attached to the lead connector 24 of the IPG 10, which is implanted a somewhat distant location from the lead, such as in the upper portion of the patient's buttocks. Typically in an SCS application, there are two leads implanted in the left and right sides of the spinal column, so that stimulation therapy can be delivered by the IPG 10 to left- and right-branching nerves from the dura 82. However, only one such lead is shown in FIG. 3 for simplicity.
Once implanted, the patient is typically put though a fitting procedure to determine effective therapy to treat the patient's symptoms. This typically occurs in a clinician's office, and may be somewhat experimental in nature. (Some aspects of fitting may also occur prior to full implantation of the IPG 10 during an external trial stimulation phase, which is discussed in U.S. Patent Publication 2010/0228324 for example).
Generally speaking, during the fitting procedure, various stimulation parameters are applied by the IPG 10 to determine what feels best for the patient, and then such stimulation parameters can then be stored in the IPG 10 as a stimulation program. Stimulation parameters can include which electrodes 16 on the lead 18 are active, the polarity of the active electrodes (i.e., whether they act as anodes (current sources) or cathodes (current sinks)), the magnitude of the current pulses applied at the active electrodes (which may comprise either a voltage or current magnitude), the duration of the pulses, the frequency of the pulses, and other parameters. These stimulation parameters can be varied by the external controller 50—either a clinician programmer or a hand-held patient controller—which wirelessly communicates with the telemetry coil 34 in the IPG 10 to change and store the parameters in the IPG 10. After a stimulation program has been set by the clinician, and the patient has left the clinician's office, the patient can modify the stimulation parameters of that program using his hand-held patient controller.
The art has recognized that patients may benefit from the use of different stimulation at different times, and in particular depending on the patient's posture or activity. This is because the position of the lead 18 may move in the epidural space 50 as the patient changes moves, e.g., from supine (on one's back), to standing, to prone (on one's stomach). This is shown by the arrows in FIG. 3. As seen, as the patient moves, the distance between the electrodes 16 and the dura 82 can change. This change in distance can warrant changes in therapy.
In the prior art, such changes in patient posture or activity were sensed by an accelerometer in the IPG 10. As is well known, an accelerometer can detect its position in three-dimensional (3D) space by assessing gravitational forces, and so can detect the 3D position of a patient in which it is implanted. According to this technique, a patient is somewhat relieved of the obligation to manually adjust his stimulation parameters when changing postures, because the IPG can recognize a change in body posture and remember the level of stimulation needed. Thus, in the prior art, an IPG 100 could sense when the patient changes posture; learn from previous experience and remember the patient's last comfortable setting for that posture; and respond by automatically adjusting stimulation to the patient's chosen setting for that posture.